isl_tab_dup: properly initialize cone field from original
isl_tab_dup: properly initialize cone field from original

Apparently this field does not get used in the copy
since it has never been properly initialized, having
been introduced in isl-0.01-85-gd5cbda1065 (isl_tab_pip.c:
incrementally build recession cone of gbr context,
Thu Oct 8 09:29:33 2009 +0200).

Reported-by: Michael Kruse <e37bdc670d6573b8890bd5bd5b982b09bd5220e8@meinersbur.de>
Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl